This invention relates to a device for turning a nut on a stud which attaches the cover to a nuclear reactor vessel.
In certain applications, large bolts or studs are pretensioned during installation, generally by hydraulic tightening devices to improve their resistance to stresses they receive during normal functioning. In the nuclear industry, this is particularly the case with studs for attaching the covers of reactor vessels. Such studs are threaded into the body of the vessel and then held under tension until cover-holding nuts on the studs are tightened downwardly against the vessel cover.
Taking into consideration the large number of studs and the possiblity of dangerous radiations, it is desirable to shorten the time required to connect the studs to the reactor vessel and place them under preliminary tension when closing the cover of the reactor vessel. It is also important to expedite the tensioning and removal of the studs as is required, for example, when the fuel elements are changed.
Apparatus for placing and tensioning studs is known, examples, thereof being described in published French patent application Nos. 2,329,414 and 2,294,795. In such devices, hydraulic tighteners bear against nuts positioned on each stud. In known devices such as those described in the French certificate of utility No. 2,208,756 or the French patent application No. 2,294,795, a laterally toothed pinion engages external circumferential gear teeth on the upper nut. During tightening and unscrewing of the tensioning nut, there is no compensation for the substantial weight of the studs, this weight being borne fully by the threads which connect the tensioning nuts to their respective studs.
An object of the present invention is to permit the tightening and unscrewing of such stud-tensioning nuts without exerting any stress on the threads of the nut. It is also an object to permit unscrewing of the tensioning nut from the stud while the respective stud is being tightened into the body of the reactor vessel.